Detection of mating, pregnancy and imminent parturition in the grasscutter
(Thryonomysswinderianus)

Phyllis Addo

Abstract

This study was undertaken to
establish methods for detecting mating, pregnancy and imminent parturition in the grasscutter to aid in the captive breeding of the species. Nineteen
female grasscutters were hand-mated and subsequently
individually caged to determine the outcome of male-female contact (i.e. mating,
conception and parturition) and the cardinal signs that accompany them. The signs of
mating were detected by monitoring changes in the perineum of the female before and after
mating; the signs of pregnancy by monitoring changes in the perineum of the female,
changes in weight gained post-mating and presence of foetusesin
utero by abdominal palpation; while the signs of imminent
parturition were detected by monitoring expectant mothers with distended abdomens for
change in feeding/drinking habits, behaviour and posture.

The findings of the study
suggest that mating in grasscutters is always manifested by vulval congestion, which is sometimes accompanied by vulvaloedema and protrusion of the
vaginal wall. Pregnancy is manifested by a definite change in body weight
four weeks after mating and by intermittent vaginal bleeding and palpation of foetusesin utero five weeks
after mating. Parturition is imminent within three days when the expectant mother stands
on only its hind legs, and it is a day away when the change in posture is combined with
frequent looks at the lower abdomen. The grasscutters give
birth to precocious young after 148-158days of gestation. Mating, pregnancy and imminent
parturition are therefore detectable in the grasscutter by
visible cardinal signs.

Introduction

The grasscutter
is a hystricomorph rodent widely distributed in the African
sub-region and exploited in most areas as a source of animal protein (Vos
1978; Asibey 1974; National Research Council 1991). Being the
preferred and most expensive meat in West Africa (Baptist and Mensah
1986; Asibey and Addo 2000), it
contributes to both local and export earnings of many West African countries (Asibey 1969; National Research Council 1991; Baptist and Mensah 1986; GEPC 1995, Ntiamoa-Baidu
1998) and is therefore hunted aggressively. At a local market for example, approximately
73 tonnes of grasscutter meat were
sold in one year, which represented more than 15,000 animals (National Research Council
1991). Unfortunately its collection from the wild is attended by destruction of the
environment, through the setting of bush fires by hunters (National Research Council 1991;
Yeboah and Adamu 1995; Ntiamoa-Baidu 1998). To address this problem, attempts are being
made in the sub-region to domesticate the grasscutter
(National Research Council 1991; Anonymous 1993) and make it more readily available, gain
economic benefit and also reduce the environmental destruction that accompanies its
collection from the wild (National Research Council 1991; Ntiamoa-Baidu
1998). The attempts have not been as successful as desired (Baptist and Mensah 1986) due to paucity of information on the biology of the
species (Aduet al
1999).

The main determinant of successful
domestication is the maintenance of reproductive competence (Zeuner 1963; Fox 1987;
Dukelow 1978; Adams 1989), therefore in investigating the
biology of the grasscutter, information that would have bearing on its successful breeding in captivity is of immediate
importance. To
facilitate the study, parameters known to enhance the
captive breeding of already-domesticated animals should
be investigated for their applicability in the grasscutter. For example, the
detection of mating, diagnosis of pregnancy and detection of imminent parturition in
laboratory (Arrington 1972) and farm (Arthur et al
1989) animals have been shown to
enhance animal production (Arrington 1972; UFAW
1989). Some of the methods used were perineal examination post-mating,
abdominal palpation, monitoring of changes in body weight during
gestation, biological pregnancy assays and unobtrusive observation of pregnant animals for
changes in behaviour and
posture as parturition approaches (Hafez 1970; Arrington 1972;Arthur et al1989; UFAW 1989). This study sought to provide
information on the reproductive biology of the grasscutter, specifically, the detection of
mating, diagnosis of pregnancy and detection of imminent parturition, using all the
aforementioned methods except biological pregnancy
assays. The methods were used in conjunction with hand-mating and individual caging
of the female before and after mating, in order to make it easier to evaluate the outcome
of each mating session, as well as facilitate better assessment of the progression of
pregnancy and manifestation of any signs of pending or approaching parturition.

This paper reports on the methods used in
detecting mating, pregnancy and imminent parturition in the grasscutter,
and the periods during which each method provides an unequivocal positive result.

Materials and Methods

Experimental animals

Twenty-eight sexually mature grasscutters
made up of 19 females and 9 males were used for the study. They formed part of a colony of
wild and laboratory-bred grasscutters maintained in the
conventional animal facility of the Noguchi Memorial Institute for Medical Research
(NMIMR).

Hand-mating and detection of mating

Grasscutters are induced ovulators (Stieret al 1991; Adjanohoun
1993; Addoet al
2001) and breed all year round (Asibey 1974) therefore no
consideration was given to the time of mating. However, though grasscutter
are inducedovulators,
they sometimes show variations in their reproductive activity or sexual cycle (Adjanohoun 1993), which is manifested by the status of their vaginal
membrane. Sometimes when sexually ready or in oestrus,
the female grasscutter may present a perforated vaginal
membrane with (sealed) or without (open) a hardened vaginal secretion.When not sexually ready or in anoestrus it may present an intact (closed)
vaginal membrane (Adjanohoun 1993). The hand-mating
process was therefore conducted taking cognisance of these
variations. Hand-mating was conducted by transferring the female to the males cage.
Prior to the transfer, the females body weight, vaginal status (open, sealed,
closed), date and time of the transfer were noted, after which it was left with the male
until it had been mated. During the females stay with the male it was examined daily
for post-pairing perineal changes namely: perforation of the
vaginal membrane (in females that presented closed or sealed vaginal membranes at the time
of pairing), nature of vaginal secretion if any and presence of a copulatory
plug in the vagina. Other mating signs looked for were copulatory
plug on the cage floor and scratches on the females trunk inflicted by the male in
its attempt to mount the female (Asibey 1974). On observing
any of the signs, the female was immediately and permanently separated from the male,
weighed, transferred to its own cage and the date and time of the appearance of the
mating-sign(s) noted. The female wasthereafter monitored either daily or weekly
for signs of fertile mating.

Pregnancy diagnosis

Pregnancy
diagnosis was conducted either daily or weekly, depending on the parameter under investigation. The daily-monitored parameters were: status of the
vaginal membrane (closed, sealed or open) and presence/characteristics of vaginal
secretion. The weekly-monitored parameters were: change in body weight and presence of
developing foetusesin utero,
which was determined by abdominal palpation (Figure 1). To conduct the palpation, the
animal was partially restrained in a restraining net designed by the author, while an
attendant held the animal firmly but gently at the shoulders. The examiner held the animal
by the tail and placed one hand between its hind legs, moved the hand gently until the
animals lower abdomen was cupped in the hand. The uterine horns were gently passed
in between the fingers and the foetuses were felt as slippery
marbles during the early stages of gestation. All the methods, except change in body
weight were used for eight weeks after mating. Animals that were diagnosed pregnant by the
end of the eighth week were transferred to maternity cages (H: 50cm, W: 40cm, L: 80cm).
Weight change was monitored until the 21st week of pregnancy because it was
considered to be the least stressful of the pregnancy diagnostic methods.

Figure 1. Diagnosing pregnancy in the grasscutter by abdominal
palpation

Detection of imminent parturition and determination
of gestation length

Pregnant
animals were monitored for peculiar signs that could be indicators of imminent delivery,
therefore those with distended abdomens were observed unobtrusively daily, from 6am to 6pm at three-hourly intervals, for change in
eating and drinking habits as well as change in behaviour and
posture. Gestation length was estimated to be from the day of the appearance of the mating
sign (day 1) to the day of parturition.

Data analyses

Statistical analysis was
conducted with the Statistical Package for the Social Sciences (SPSS, Standard version,
Release 10.01) (SPSS Inc. 1989-1999). The mating data were analysed by the cross-tabulation procedure as follows: The association between mating and mating
signs was determined using the Pearsons chi square statistic, while the degree of
the association for each sign (scratch, vulval oedema and vulval congestion) was
determined by the Phi coefficient. The predictability of mating by the principal mating
sign (vulval congestion) was computed by the Phi, Lambda, Goodman and Kruskal tau and
uncertainty coefficients. The two principal signs observed post-mating (vulval oedema and
vulval congestion) were compared by the Pearsons chi square statistic to determine
if there was a difference in their use as indicators of successful mating. The data on
pregnancy diagnosis was analysed by the cross-tabulation
procedure as follows: The Pearsons chi square statistic was used to determine if
there was any association between intermittent vaginal bleeding and pregnancy. The use of
intermittent vaginal bleeding as a predictor of pregnancy was analysed by the Phi, Lambda,
Goodman and Kruskal tau and uncertainty coefficients. The Pearsons chi square
statistic was used to determine if there was any association between gestational age and
the results of abdominal palpation on one hand and change in body weight on another hand
within the first eight weeks of pregnancy. The Pearsons chi square statistic was
also used to compare the performance of the two tools (abdominal palpation and change in
body weight) as pregnancy diagnostic methods. The changes in body weight data were further
analysed by the case summaries procedure to compute averages of the weekly weights gained
by the colony of pregnant grasscutters during the 21week gestation period. The weight data
were thereafter log transformed after screening for normality and homogeneity of variance.
The weights gained by individual females during pregnancy were compared using one-way
analysis of variance (ANOVA). ANOVA and post hoc multiple comparisons were used to compare
the differences in the weekly weights gained by the entire colony of pregnant grasscutters
during the 21-week period. Pearson correlation coefficient was used to determine if there
is any relationship between weight gained and age of pregnancy, while linear regression
was used to determine if age of pregnancy is a predictor of weight gained during
pregnancy.

Results

Mating signs

Eighteen (94.7%) of
the 19 females presented obvious changes in the perineal region namely; vulval congestion
(figure 2) or vulval
congestion with vulval oedema, and occasional protrusion of the anterior walls of the
vagina. The mating signs disappeared within 3 hours of the females separation from
the male.

Figure 2.Vulval congestion observed in a grasscutter after mating

Two (10.52%) of the
19 animals presented scratches on the trunk and one of them maintained an intact vaginal
membrane throughout its stay with the male. The scratches on the female that failed to
mate were deep wounds that needed veterinary attention. None of the animals given for
mating presented a copulatory plug in the vagina or cage tray. Vulval congestion (100%)
was found to be positively associated with mating (?2 = 20.000, P<0.001; Phi
= 1.000, P<0.001) and a perfect predictor of successful mating (Phi = 1.000,
P<0.001; Lambda = 1.000, P<0.001; Goodman and Kruskal tau = 1.000, P<0.001;
Uncertainty coefficient = 1.000, P<0.001). Surprisingly, no association (?2 =
1.955; P>0.05) was found between vulval oedema (72.2%) and mating. Scratches (10.5%)
were found to be negatively associated with mating (?2 = 9.474, P<0.01; Phi
= -0.688, P<0.01).
The details of the changes that occurred after pairing the male and female are presented
in Table 1.

Pregnancy diagnosis by perineal changes

Perforation and closure of the vaginal membrane

The vaginal membranes of the 18 successfully mated females
reformed between 8-27days (14.4 ± 5.32 days) after appearance of the mating sign(s). The
closure of the vagina occurred irrespective of whether the female conceived or not. The
vaginal membranes of the 18 females later perforated, between 30-42 days (35.22 ± 4.56 days) after mating and was irrespective of whether
the female conceived or not.

Perforation of the vaginal membrane with intermittent vaginal bleeding

Pregnancy diagnosis by change in body weight

The body
weights of the 18-mated females fluctuated until the third week after mating. During the
three-week period, 16 (88.9%) of the 18 females had an average weight change of 41.2 ±
33.2 g (0-150 g), while two (11.1%) had an average weight change of 1.67 ± 5.16

Table 2. Average weight gained during pregnancy by 14 grasscutters that littered

Week post-mating

Average weight gained

± SD (g)/ [Weight range]

Week post-mating

Average weight gained

± S.D (g)/ [Weight range]

1

25.00 ± 23.45

[0  60.00]

12

445.17 ± 152.36

[220.00  601.00]

2

33.33 ± 27.33

[0  80.00]

13

493.83 ± 171.95

[244.00  680.00]

3

65.83 ± 36.66

[10.00  105.00]

14

558.50 ± 161.42

[316.00  750.00]

4

122.00 ± 39.80

[80.00  182.00]

15

623.67 ± 154.50

[396.00  820.00]

5

164.50 ± 36.02

[120.00  207.00]

16

692.67 ± 149.10

[476.00 ± 894.00]

6

234.17 ± 70.35

[140.00  320.00]

17

771.67 ± 150.54

[556.00  966.00]

7

283.33 ± 84.31

[170.00  380.00]

18

845.17 ± 155.94

[636.00  1040.00]

8

311.33 ± 81.56

[200.00- 384.00]

19

928.67 ± 165.80

[722.00  1130.00]

9

344.33 ± 88.46

[200.00  446.00]

20

1016.67 ± 176.63

[800.00  1220.00]

10

369.50 ± 113.70

[200.00  501.00]

21

1098.00 ± 183.87

[860.00  1310.00]

11

405.33 ± 126.88

[220.00  542.00]

Mean ± SE = 468 ± 71.2

SD: Standard deviation; SE: Standard error of mean

The 14 females
did not differ significantly (P>0.05) from each other in weight gained during the
21week gestation period; though two experienced partial foetalresorption. One of the two stagnated at 200 g for three weeks
(8th  10th week), after which it steadily gained a total of
1232 g at the 21st week, and the other lost 160 g from the 9th to
the 14th week, after which it also steadily gained a total of 902 g in the 21st
week. The remaining two of the 16 females experienced a total cessation of growth (total foetalresorption) at the 11th
(260 g) and 14th week (410 g) of pregnancy. The two females that showed no
appreciable change in weight the first three weeks after mating continued to maintain a
low weight change (18.4 ± 10.0) to the end of pregnancy. The progression of gestation in
the 14 females showed that statistically significant weight gains were made in the 3rd,
4th, 7th, 9th, 13th, 15th, 16th,
17th, 18th, 19th, and 20th weeks of pregnancy.
The significant change in the third week was the beginning of the turning point between
pregnant and non-pregnant status; while the significant change in the fourth week was the
point of unmistakable distinction between pregnant and non-pregnant status. From the 13th
week the foetuses showed consistent growth up till the 20th
week of gestation. A strong positive correlation was found between age of pregnancy and
weight gained (r = 0.93, P<0.01). Age of pregnancy was computed to be a good predictor
of weight gained during pregnancy. The dependence of weight gained, on age of pregnancy
was described by:

Weight gained
= -102 + 51.9*(gestational age)

The categorization of females into pregnant and non-pregnant states (pregnancy diagnosis
by change in body weights) differed significantly amongst the weeks (?2 = 13.3,
P>0.005), with the highest (maximum) categorization rate being recorded in the fourth
week of gestation. Subsequently, the fifth to the eighth week turned out to be weeks of
confirmatory diagnosis.

Pregnancy diagnosis by abdominal palpation

The foetuses were felt as slippery
marbles of varying sizes two weeks after appearance of the mating sign(s). The diagnosis
was categorized as tentative at this stage, due to the semblance of the foetuses to faecal
pellets, which could also be felt during the palpation. In the third week, the paired
uteri were as one swollen mass with an elongated content and in the fourth week as a
voluminous bag of soft consistency. In the fifth week the uteri still maintained their
voluminous nature but contained long rods. In the sixth week the uteri became
comparatively less voluminous and the foetuses were felt as distinct short rods, a pattern
that continued till the eight week. The detection rates of pregnancy by abdominal
palpation differed significantly amongst the weeks (?2 = 19.429 P>0.001),
and the highest (maximum) detection rate was recorded in the third week of gestation.
Consequently, the fourth to the eighth week turned out to be confirmatory diagnosis.
Comparison of pregnancy detection rates by abdominal palpation and change in body weight
showed that there was no difference between the two methods for the eight-week monitoring
period (?2 = 0.000, P>0.05). Analysis of individual week rates for the two
methods also showed no significant differences: week one: ?2 = 2.33, P>0.05;
week two: ?2 = 0.57, P>0.05; week three through week eight: ?2 =
2.15, P>0.05. A comparison of the pregnancy-related features observed using the four
pregnancy diagnostic methods during the eight-week monitoring period is provided in Table
3.

Table 3: Comparison of
results from four pregnancy diagnostic methods used on 14 grasscutters
that littered

Period

Vaginal membrane status and
vaginal secretion

Change in body weight (g)

Status of pregnant uterus (Abdominal palpation)

Week 1

Closed

25.0 ± 23.4

Slippery marbles

Week 2

Closed

33.3 ± 27.3

Slippery marbles

Week 3

Closed

65.8 ± 36.7

#Swollen mass with elongated
content

Week 4

Open

122 ± 39.8

#Indisputable weight gain

Soft voluminous bag

Week 5

Open

#Intermittent bleeding

164.5 ± 36.0

Voluminous bag containing long
rods

Week 6

Open

234.2 ± 70.3

Fairly voluminous bag containing
short rods

Week 7

Closed

283± 84.3

Fairly voluminous bag containing
short rods

Week 8

Closed

311 ± 81.6

Fairly voluminous bag containing
short rods

#Stage at which an unequivocal
positive result is obtained

Signs of imminent parturition, parturition and gestation length

The
abdomen of the pregnant animals distended and took on the shape of a rugby
ball in the 4th month. Nine (64.3%) of the 14
expectant mothers walked on only the hind limbs (personally termed the "penguin
posture") three days before delivery and combined the penguin posture
with frequent downward looks at the lower abdomen a day before delivery. Parturition
occurred between 148-158 days (152 ± 2.98 days) after appearance of the mating sign. The
parturition process could not be observed in all the animals except two. The two littered
whilst standing on only the hind limbs. The mothers ate the placenta after the delivery of
each baby, before proceeding on to deliver the next baby. The neonates were born fully
haired with the eyes open. They stood by their mothers during the delivery of their
littermates and followedthe mother about
within minutes of their delivery, which took approximately 32-40 minutes.

Discussion

The
findings of this study show that mating, pregnancy and imminent parturition are visibly
manifested in the grasscutter and therefore can be detected to aid in the practical
management of grasscutter breeding programmes. Asibeys (1974) assertion that
scratches on the trunk of female grasscutters are signs of mating was not confirmed by
this study. Mating scratches were observed in only two of the nineteen females given for
mating, one of which also presented perineal congestion and oedema. The female that had
only scratches (deep wounds) maintained an intact vaginal membrane after weeks of stay
with the male. Statistically it was shown that scratches and mating were strongly
inversely related (Phi = - 69%) suggesting that the presence of scratches may rather be an
indication of non-successful mating. It could be hypothesized that probably females that
persistently resist the males are those that receive scratches, and not necessarily those
that have been mated. In the bush or in wider enclosures, the chances of prolonged
courting and frequent running away from the male are increased, which lead to a more
frequent struggle between the couple, and hence the greater number of females with
scratched trunks observed in Asibey's collections from the wild. Probably it is for the
same reason that fewer females with scratches were recorded in this study since the cages
were of a smaller dimension (H40cm x L50cm x W40cm). This goes to support Adjanohoun's
(1993) recommendation that it is preferable to use cages of reduced dimensions (W: 50cm L:
65cm H: 37cm) to protect the female from being wounded during the violent phase of
courtship and also provide the male a more congenial environment i.e., a reduced area to
enable it court more efficiently by preventing the female from slipping away. The smaller
enclosure would invariably increase the male-female contacts, which are likely to favour
the appearance of oestrus (Adjanohoun 1993) since the grasscutter is an induced ovulator
(Addo et al 2001).

The most consistent and reliable sign of mating in the
grasscutter according to the findings of this study is perineal congestion, since it was
the only sign that was consistently observed in all mated females among the post-mating
signs observed. This finding goes to confirm Adjanohouns report (1993) that a strong
and brief congestion of the ano-genital zone of the grasscutter is observed immediately
after coitus. The briefness of the congestion was confirmed by this study, and since the
perineal sign is of a short duration, females given for mating should be examined daily
for its detection. Though one of the females that showed perineal signs did not conceive,
it does not mean that the sign is not reliable, because about
20-25% of female rabbits fail to conceive following coitus due to failure to ovulate which
in turn is due to a deficiency of LH (Fox and Krinsky 1968), a situation that might have
arisen in the case of the grasscutter. Above all, post-mating vulval congestion also turned out to be a perfect predictor of successful
mating by all the measures examined (Predictability = 100%, P <0.001).Surprisingly, vulval oedema could
not be confirmed statistically as a mating sign. This outcome may be because vulval oedema
was indeed an incidental finding or that the sample size was not large enough to allow its
statistical confirmation.

Pregnancy
was successfully diagnosed employing three methods, each yielding an unequivocal result at
a particular time. First and foremost, the present findings suggest that the reformation
of the vaginal closure membrane after mating should not be considered a sign of
conception, as assumed by some (Asibey 1974), since the
vaginal closure membrane was observed to reform in all mated females between the 8th and
27th day after mating, irrespective of the outcome of the mating. Furthermore,
irrespective of the outcome of mating, the vaginal membrane re-ruptured between 30-42 days
post-mating, a phenomenon that sometimes occurs mid-pregnancy
in guinea pigs. The phenomenon in the guinea pig is attributed to the surge of
progesterone and increase in relaxin production (Zarrow 1947; Jagiello 1965). The same
explanation may hold for the occurrence of the phenomenon in the grasscutter.
Since the grasscutter is an induced ovulator,
mating results in ovulation and the formation of corpora lutea
with consequential production of progesterone in all mated females, leading to the rupture
of the vaginal membrane, irrespective of the mating outcome. It was also demonstrated in
the study that the vaginal membrane of all the
pregnant animals perforated with intermittent bleeding five weeks after mating. Fourteen
(87.5%) of the sixteen animals that bled, delivered, while those that did not bleed, were
not diagnosed pregnant by the other two methods (abdominal palpation and weight gain) and
above all, never delivered, suggesting that the bleeding only occurs in those that are
pregnant. Hoar et al(1957) considered vaginal
bleeding in the guinea pig to be a sign of embryo resorption
or abortion of the litter, whilst in monkeys it is considered a sign of implantation (Valerioet al
1969). The findings of this study suggest that the observation made in the grasscutter in the fifth week of gestation may be implantation
bleeding, rather than embryo resorption or abortion. The
reason being that all the grasscutters that bled continued to
gain weight normally, and even though two stopped gaining weight, the set back occurred in
the eleventh and fourteenth week of gestation, times that were quite far removed from the
fifth week. The cessation in the eleventh and fourteenth week must have been total embryo resorption, while that which occurred from the eighth to the tenth
week must have been partial embryo resorption. To
buttress this stand, intermittent vaginal bleeding was statistically shown to be a perfect
predictor of conception by all the measures examined (Predictability = 100%, P <0.001).

Pregnancy diagnosis by abdominal palpation was performed
from the first to the eight week after mating and yielded unequivocal results the third
week after mating. Use of the technique before the third week of pregnancy should be done
appreciating the difference between embryos and faecal
pellets. The latter are hard and more fixed with respect to mobility. The embryos on the
other hand, a few days post-coitus are felt between the fingers as small, slippery
marbles, which get progressively bigger and elongated as the pregnancy advanced. The
technique should be done gently so as not to disturb the pregnancy, since grasscutters are prone to embryo resorption,
which is an unelucidated phenomenon.

Pregnancy diagnosis by monitoring changes in body weightwas
found to be very reliable. It brought out an evident difference between the pregnant and
non-pregnant in the fourth week of a five and a half month long pregnancy. It is also a
method worth employing weekly until delivery, since it efficiently reveals both partial
and total resorption, a reproduction problem of grasscutters (Asibey 1974; Adu and Yeboah 2000). Above all, it is
an easier and safer method of diagnosing pregnancy in the grasscutter.
Special training is not required to enable one to use this method and could therefore be
conveniently practiced by the semi-literate farmer.

The findings of this study suggest that the grasscutter manifests cardinal signs of imminent parturition. The
signs are both unique and conspicuous and will therefore be easily recognised
by all categories of grasscutter breeders, the young, the old,
the literate and illiterate. Such conspicuous changes which appear days before parturition, will provide the breeder adequate time for proper
preparation and, in good time, to institute timely managerial preparations that would cut
down on losses, which could usually result from inappropriate caging, feeding, mishandling
and obtrusive observation. In all species studied, the onset of parturition is manifested
by the occurrence of myometrial activity (Arthur et al 1989). Most probably the frequent
glances at the lower abdomen by the grasscutter during the
last 24 hours of pregnancy were due to increased myometrial
activity of the labour process. Parturition in the grasscutter as is also usual in most species (Arrington 1972), is
very infrequent during the day and that is why only two females were observed in this
study. However, when stumbled upon it is found to be normally over within 32to 40 minutes, a finding which is in agreement
with Asibeys report (1974) that grasscutters
delivered within 57 minutes.

The findings
on gestation length in this study did not confirm the
observations by Ewer (1960) and Asibey (1974), who
reported gestation lengths of 70 days and 108 ± 5.3
days, respectively. The finding of this study (152
± 2.98 days [148 - 158 days]) are in agreement with reports by Mensah and Baptist (1986) [152 ± 2 days], Adjanohoun
(1988) [156 ± 3 days] and Stieret al (1991) [152 days]. The long gestation
length observed in the grasscutter is typical of hystricomorph rodents (Weir 1974) and therefore cannot be considered
unusual.

Conclusion

The findings
of this study have shown that mating, pregnancy and imminent parturition are manifested
visibly in the grasscutter and therefore can be detected as an
aid in the practical management of grasscutter breeding programmes.

·Successful
mating in grasscutters is manifested by vulval
congestion sometimes accompanied by vulvaloedema and protrusion of the vaginal wall.

·Pregnancy
can be diagnosed by abdominal palpation three weeks after mating, by a definite change in
body weight four weeks after mating and by intermittent vaginal bleeding five weeks after
mating.

·Imminent
parturition is manifested by the expectant mother adopting the penguin posture
three days before delivery and a combination of the penguin posture with
frequent looks at the lower abdomen a day before delivery.

·The grasscutter delivers precocious young after 148-158days of
gestation.

Acknowledgements

The author thanks the Noguchi Memorial Institute for Medical Research
for funding the study. The author also acknowledges the technical assistance of Messrs
Emmanuel AttaTioh, Samuel Mensah, Daniel Osei-Boakye, David Appiah for the care and management of the grasscutters,
Atu Jones for constructing the grasscutter
maternity cages, Messrs Alfred Dodoo and Isaac Hudson Odoi for
photography.